The present invention relates to a method for transmitting voice data over various types of networks in which user data are transmitted via a transmission link of a circuit-switched data transmission network. The user data transmitted via the transmission link are distributed to data packets and forwarded via a packet transmission network.
A known method is carried out in an interworking unit which connects a packet transmission network and a circuit-switched network, see Standard H.323 (02/98) “Packet Based Multimedia Communications Systems” of the ITU-T (International Telecommunication Union-Standardization Sector Telecommunication). The interworking unit is also called a gateway in the Standard.
In the packet transmission network, the data are forwarded on the basis of data packets. However, methods are also known for forwarding data packets in circuit-switched networks. The data packets have a packet header in which the address of a destination and the address of the sender are located. There is also a data packet body in which the user data are transmitted. Typical examples of packet transmission networks are networks operating in accordance with the Internet protocol, or ATM (Asynchronous Transfer Mode) networks.
During the transmission of voice data in circuit-switched networks, i.e. in networks in which a transmission link is permanently allocated to a connection for the duration of the circuit-switched connection, user data are also transmitted in silence intervals. However, these user data are redundant for understanding the conversation. From circuit-switched networks, various measures for suppressing the forwarding of user data in silence intervals are known which, however, cannot be easily transferred to packet transmission networks or to the transition between a circuit-switched network and a packet transmission network because they only relate to the better utilization of transmission channels.
It is an object of the present invention, therefore, to specify, for the transmission of voice data over various types of data transmission networks, a simple method and apparatus in which the transmission of redundant data is restricted.